[PATCH 5/8] qdev: improve find_device_state() to distinguish simple not found case
Vladimir Sementsov-Ogievskiy
vsementsov at virtuozzo.com
Thu Sep 16 12:54:39 UTC 2021
16.09.2021 13:48, Markus Armbruster wrote:
> Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com> writes:
>
>> We'll need this for realizing qdev_find_child() in the next commit.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
>> ---
>> softmmu/qdev-monitor.c | 48 +++++++++++++++++++++++++++++-------------
>> 1 file changed, 33 insertions(+), 15 deletions(-)
>>
>> diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
>> index 721dec2d82..0117989009 100644
>> --- a/softmmu/qdev-monitor.c
>> +++ b/softmmu/qdev-monitor.c
>> @@ -819,7 +819,12 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
>> object_unref(OBJECT(dev));
>> }
>>
>> -static DeviceState *find_device_state(const char *id, Error **errp)
>> +/*
>> + * Returns: 1 when found, @dev set
>> + * 0 not found, @dev and @errp untouched
>> + * <0 error, or id is ambiguous, @errp set
>> + */
>> +static int find_device_state(const char *id, DeviceState **dev, Error **errp)
>> {
>> Object *obj;
>>
>> @@ -835,17 +840,16 @@ static DeviceState *find_device_state(const char *id, Error **errp)
>> }
>>
>> if (!obj) {
>> - error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
>> - "Device '%s' not found", id);
>> - return NULL;
>> + return 0;
>> }
>>
>> if (!object_dynamic_cast(obj, TYPE_DEVICE)) {
>> error_setg(errp, "%s is not a hotpluggable device", id);
>> - return NULL;
>> + return -EINVAL;
>> }
>>
>> - return DEVICE(obj);
>> + *dev = DEVICE(obj);
>> + return 1;
>> }
>>
>> void qdev_unplug(DeviceState *dev, Error **errp)
>> @@ -894,16 +898,25 @@ void qdev_unplug(DeviceState *dev, Error **errp)
>>
>> void qmp_device_del(const char *id, Error **errp)
>> {
>> - DeviceState *dev = find_device_state(id, errp);
>> - if (dev != NULL) {
>> - if (dev->pending_deleted_event) {
>> - error_setg(errp, "Device %s is already in the "
>> - "process of unplug", id);
>> - return;
>> + int ret;
>> + DeviceState *dev;
>> +
>> + ret = find_device_state(id, &dev, errp);
>> + if (ret <= 0) {
>> + if (ret == 0) {
>> + error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
>> + "Device '%s' not found", id);
>> }
>> + return;
>> + }
>>
>> - qdev_unplug(dev, errp);
>> + if (dev->pending_deleted_event) {
>> + error_setg(errp, "Device %s is already in the "
>> + "process of unplug", id);
>> + return;
>> }
>> +
>> + qdev_unplug(dev, errp);
>> }
>>
>> void hmp_device_add(Monitor *mon, const QDict *qdict)
>> @@ -925,11 +938,16 @@ void hmp_device_del(Monitor *mon, const QDict *qdict)
>>
>> BlockBackend *blk_by_qdev_id(const char *id, Error **errp)
>> {
>> + int ret;
>> DeviceState *dev;
>> BlockBackend *blk;
>>
>> - dev = find_device_state(id, errp);
>> - if (dev == NULL) {
>> + ret = find_device_state(id, &dev, errp);
>> + if (ret <= 0) {
>> + if (ret == 0) {
>> + error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
>> + "Device '%s' not found", id);
>> + }
>> return NULL;
>> }
>
> Awkward.
>
> Before, find_device_state() either finds something (and returns it) or
> doesn't (and sets @errp).
>
> Afterward, it can fail to find in two ways, and only one of it sets
> @errp. The existing callers laboriously fuse the two back together.
> The next commit adds a caller that doesn't.
>
> Failure modes that need to be handled differently are often the result
> of a function doing too much. Let's have a closer look at this one
> before the patch:
>
> static DeviceState *find_device_state(const char *id, Error **errp)
> {
> Object *obj;
>
> if (id[0] == '/') {
> obj = object_resolve_path(id, NULL);
>
> This interprets @id as a QOM path, and tries to resolve it.
>
> On failure, @obj becomes NULL. On success, it points to an object of
> arbitrary type.
>
> } else {
> char *root_path = object_get_canonical_path(qdev_get_peripheral());
> char *path = g_strdup_printf("%s/%s", root_path, id);
>
> g_free(root_path);
> obj = object_resolve_path_type(path, TYPE_DEVICE, NULL);
> g_free(path);
>
> This interprets @id as qdev ID, maps it to a QOM path, and tries to
> resolve it to a TYPE_DEVICE. Fails when the path doesn't resolve, and
> when it resolves to something that isn't a TYPE_DEVICE. The latter
> can't happen as long as we put only devices under /machine/peripheral/.
>
> On failure, @obj becomes NULL. On success, it points to a TYPE_DEVICE
> object.
>
> }
>
> if (!obj) {
> error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
> "Device '%s' not found", id);
> return NULL;
> }
>
> if (!object_dynamic_cast(obj, TYPE_DEVICE)) {
> error_setg(errp, "%s is not a hotpluggable device", id);
> return NULL;
> }
>
> Unclean.
>
> If we somehow ended up with a non-device /machine/peripheral/foo, then
> find_device_state("foo", errp) would fail the first way, but
> find_device_state("/machine/peripheral/foo", errp) would fail the second
> way. They should fail the exact same way instead.
>
> return DEVICE(obj);
> }
>
> Better:
>
> static DeviceState *find_device_state(const char *id, Error **errp)
> {
> Object *obj;
> DeviceState *dev;
>
> if (id[0] == '/') {
> obj = object_resolve_path(id, NULL);
> } else {
> obj = object_resolve_path_component(qdev_get_peripheral(), id);
> }
>
> if (!obj) {
> error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
> "Device '%s' not found", id);
> return NULL;
> }
>
> dev = (DeviceState *)object_dynamic_cast(obj, TYPE_DEVICE);
> if (!dev) {
> error_setg(errp, "%s is not a hotpluggable device", id);
> return NULL;
> }
>
> return dev;
> }
Looks simpler)
>
> I'll post this as a cleanup patch.
>
> Note that this function does two things, one after the other, namely
> 1. resolve a "qdev ID or qom path" string, and 2. convert to
> TYPE_DEVICE, with error checking.
>
> Factor out the core of 1. into its own helper resolve_id_or_qom_path(),
> and the next commit can do something like
>
> obj = resolve_id_or_qom_path(parent_id);
> if (!obj) {
> return 0;
> }
>
> dev = object_dynamic_cast(obj, TYPE_DEVICE);
> if (!dev) {
> error_setg(errp, ...);
> return -EINVAL;
> }
>
Thanks for working that out, I'll go this way in v2
--
Best regards,
Vladimir
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